The value of invertebrates as indicators of ancient woodland and especially pasture woodland

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WOOD FOR THE TREES

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THE VALUE OF INVERTEBRATES AS INDICATORS OF ANCIENT WOODLAND AND ESPECIALLY PASTURE WOODLAND KEITH ALEXANDER What is a wood? It may seem odd to ask such a question but the answer may be different in different circumstances. A basic broad definition might be: a concentration of trees, shrubs and other plants which have a character unique to that concentration - it is the concentration that makes the wood not the plants concerned. Special plants and animals may be associated which are not normally found where the same species of trees and shrubs occur in more isolated situations. This uniqueness of the flora and fauna is related to a number of features, but especially microclimate and - very importantly - management history. So basically we are talking about a concentration of trees. But there is a large spectrum of tree density possible, from dense closedcanopy through to very sparsely wooded. Certain woodland plants and animals may prefer particular densities of trees, particular light or shade levels. While the ecology of dense stands of trees, ie the conventional view of "woods", is the focus of much study, the sparser types of woodlands have been much neglected and are consequently poorly understood by most naturalists, ecologists, and conservationists - the dynamics of woodland communities in the more open situations is a particular problem area. Just as the term wood means different things to different organisms, so ancient woodland occurs in a wide variety of forms - viewed both from the perspective of the habitat requirements of the woodland organisms and from the management history point of view. Many species are associated with ancient woods because of their stability of damp shady habitat, while others are there for the long history of availability of timber in certain stages of decay. The shady habitat species are found in the denser ancient woodlands while the deadwood requiring species are found in ancient pasture-woodlands where the historic land-use wasn't primarily timber production, but pasture. Rackham (1996) has told us about the various traditions of tree management in Britain - emphasizing the importance of management history on the plant and animal communities. All sites effectively have unique management histories, although distinct patterns are apparent. If all are unique then, ideally, all should be conserved for all of their features. But this is impossible with all the pressures on the countryside. Conservationists need to assess the relative importance of different woodlands, to prioritise both protective measures and management plans. Ancient Woodland Indicators We know that where there has been a long history of woodland cover - ancient woodlands in the broader sense - species-richness is generally greatest. Those species or groups of species which are more or less unique to long-established woods have been used as "Ancient Woodland Indicators", and inter alia as indicators of habitat quality. The Indicator Species approach is an extremely valuable tool in site assessment. It identifies target species for survey, and thereby avoids the need for fĂźll Trans. Suffolk Nat. Soc. 32 (1996)


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The value of invertebrates as indicators of ancient woodland and especially pasture woodland by Suffolk Naturalists' Society - Issuu